A radio receiver is sensitive to radio signals in its operational frequency band. The operational frequency band is typically divided into a plurality of channels, the channels being non-overlapping within the operational frequency band. Nonetheless, a transmitted signal from a radio transmitter located in the same aircraft as the radio receiver interferes with the radio receiver, even when it uses different channels. Specifically, the transmitted signal is received by the radio receiver at high signal strength due to close proximity to the radio transmitter. This causes interference that distorts or blocks reception in the radio receiver. To reduce this interference, the prior art connects the radio transmitter and radio receiver by a control line that is activated by the radio transmitter to desensitize the radio receiver for the duration of a transmitted signal. The radio receiver is thus desensitized across its entire operational frequency band, reducing receiver performance but not preventing interference. Often, the interference and degraded radio receiver performance is unacceptable to a pilot.
In another technique of the prior art, the radio receiver attempts to reduce interference from the radio transmitter by utilizing narrow band-pass filters tuned to frequencies for a selected channel. This technique, however, prevents reception and output of multiple channels simultaneously, a desirable feature of modern radio receivers.